A feeler connection is a short-lived outbound connection that solely begins up after your node has established the required 8 outbound connections and a pair of block-relay-only outbound connections. The aim of a feeler connection is to commonly check addresses from the “new” desk to see if they’re connectable bitcoin nodes. Primarily, the feeler connection cleans the trash out of “new” and populates the “tried” desk with legitimate addresses.
- The “new” desk incorporates untested addresses that the node has discovered about from the gossip community.
- The “tried” desk incorporates addresses that the node has efficiently linked to.
Each 2 minutes the feeler connection will do certainly one of two issues:
- Pull a random peer from the eviction buffer (checklist of addresses thought-about for eviction as a result of a brand new peer is mapped to the identical slot in “tried”). Take a look at the deal with by making an attempt to hook up with it and, if profitable, take away that entry from the buffer. If this deal with is just not connectable, evict it from “tried” and change with a unique deal with (beforehand pulled from “new”).
- If the eviction buffer is empty, check a random connection from “new” and, if profitable, transfer it to “tried”. If unsuccessful, replace the deal with connection statistics accordingly. Tangentially, if an deal with fails to attach sufficient instances (amongst different standards) it will likely be labelled “horrible”. If an incoming deal with collides with a horrible deal with, the horrible deal with will probably be evicted from the “new” desk.
Feeler connections are disabled when no new blocks have been acquired for half-hour. On this case, the feeler connection is turned off and its connection slot is used each 10 minutes to attempt to discover a node that is aware of a couple of new block. That is to attempt to detect and circumvent a community partition with out overloading the variety of inbound connection slots obtainable on the community. As soon as a brand new block is found, the feeler connection reverts to cleansing out the eviction buffer and the “new” desk.
Historical past
Feeler connections are one of many prompt countermeasures of the paper “Eclipse Assaults on Bitcoin’s Peer-to-Peer Community” and have been launched with PR#8282 to extend the variety of on-line addresses within the tried desk and later PR#9037 carried out the test-before-evict performance.